Nigeria's main labor union is calling for a general strike next week to demand better pay. The threat of a strike is adding to concerns about stability in Nigeria ahead of the April 19 presidential elections.

The Nigeria Labor Congress has called on its members to go on strike indefinitely, starting Tuesday.

The call came as workers vent their anger over what union officials say is the government's failure to raise wages after it agreed to do so last year.

The strike may include workers in Nigeria's large oil sector, raising fears that oil exports may drop further.

Daily production is already down by more than a third due to fighting that erupted earlier this month between ethnic Ijaws and the Nigerian military in the Niger River delta.

Foreign oil companies shut down operations, citing concern for the safety of their employees.

Although Ijaw militants have ceased their attacks, companies this week said they will continue to suspend operations until the safety of their workers can be assured.

Analysts say the calls for a strike further add to concerns about stability in Nigeria ahead of April 19 elections in which President Olusegun Obasanjo is to seek a second term.